Nutrition is best defined as the utilization of foods by living organisms. The science of human nutrition has been steadily studied and developed as a key area of life science: up to the early 1800's, it had focused on energy metabolism of three basic nutrients falling into the classes of carbohydrates, proteins and lipids; and, since the discoveries of vitamin B in 1911 and threonine in 1935, micronutrients such as vitamins, essential amino acids and minerals had been successively discovered. On the other hand, studies on the metabolism in human body have been actively carried out since latter 1930's, with the aid of biochemical technique employing radioisotopes; and, the concept of metabolic control on molecular/biochemical level, based on said studies, became clearly established.
Under the circumstances, many different types of food can satisfy the nutritional needs of humans, even though they differ in the composition ratios of basic nutrients; and foodstuffs have been subjected to a series of nutritional tests to warrant what is acceptable for human body in light of nutrition. Accordingly, it has become natural that edibility of foodstuffs be assured after obtaining convincing nutritional results grounded on said tests.
Meanwhile, a large number of milk products has been produced and markets and consumers have been puzzled about choosing proper milks. At present, milks classified as following are commercially available: first, raw cows' milk (or organic milk) comprising around 3.3% fat obtained from milk cows; secondly, processed cows' milks, e.g., half-fat milk (.about.1.5% fat), low-fat milk (.about.1% fat), and fat-enriched milk (.about.4.5% fat). In this connection, more than 300 kinds of milk products comprising vitamin A and D-enriched milk, flavored milk, pasteurized milk, UHT (ultra-high temperature) sterilized milk and soybean milk made of soybean (see: U.S. Patent No. 3,941,890; A. I. Nelson et al., J. Food Science, 41:57 (1976)), have been spread all over the world. Milk products, though they are of significance in a sense of micronutrients which play a vital role in human metabolism, have been consumed without consideration of nutritional status of an individual. Moreover, some kinds of them have been consumed unconditionally, without evaluation of nutrition by nutritional tests employing animals.
Accordingly, needs have continued to exist for the establishment of a standard for choosing preferable milks considering consumer's nutritional status and the development of a nutritious milk product comprising preferred components and composition ratio thereofs in light of human nutrition.